1. Field of the Invention
The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a cylindrical lithium secondary battery having a structure suitable for mass production, and to a method of manufacturing the same.
2. Description of the Prior Art
Instead of a battery using an aqueous electrolyte, such as a lead battery or nickel cadmium battery, a secondary battery using a non-aqueous electrolyte has been used. As compared with a conventional secondary battery using an aqueous electrolyte, a non-aqueous electrolyte secondary battery has a large volume or a large density in weight and capacity. In addition, since high voltage can be obtained, the non-aqueous electrolyte secondary battery is expected to be used for various uses, for example, a power supply for not only a small-sized equipment but also for a large-sized apparatus.
As typified by a lithium ion secondary battery using an anode to which lithium can be doped or from which lithium can be de-doped, and a cathode containing transition metal oxide, the non-aqueous electrolyte secondary battery is manufactured in the following manner. A belt-shaped anode made of a belt-shaped anode collecting body coated with an anode active material and a belt-shaped cathode made of a belt-shaped cathode collecting body coated with a cathode active material are laminated together with two separators to form a laminate. The laminate is spirally wound to form a cylindrical battery element called a jelly roll. The jelly roll is provided with cathode and anode inner leads and is housed in a battery can so as to be electrically connected to the outer terminal of the battery can. Then, a predetermined electrolyte is injected into the battery can prior to sealing the battery can.
Such a cylindrical battery element is superior in sealing property. Moreover, since any portions are brought into contact with each other under an equal pressure, the cylindrical battery has a feature that it is possible to perform a uniform battery reaction irrespective of a place of the battery element. Thus, not only in a portable secondary battery, but also in use of a large battery used for the purpose of generating large current, the cylindrical battery occupies an important position, and is expected also as a large battery for a power source of an electric car, an electrically assisted bicycle, or the like.
An example of such a cylindrical battery is disclosed in the U.S. Pat. No. 4,943,497, which is structured such that the foregoing spirally wound battery element or a jelly roll is housed in a cylindrical battery can. An external cathode terminal member is attached to a sealing side through an insulating gasket, and the battery can is used as an anode terminal. An anode inner lead of the jelly roll is electrically connected to an inner wall of the battery can, and a cathode inner lead of the jelly roll is electrically connected to the external cathode terminal member. The cathode terminal member has a structure provided with a safety vent for releasing an inner pressure at the time of an abnormal pressure rise in the inside of the battery can, and a cathode inner lead is welded to the safety vent to make electrical connection between the battery element and the external terminal. Like this, for the purpose of making conduction between the inner lead and the external terminal, instead of directly connecting both, electrical conduction is made through a conductive connecting member such as the safety vent. As a welding operation for that, it is necessary to weld a battery header to the cathode lead before sealing.
In the above mentioned U.S. patent, after the center of the safety vent and the tip end of the cathode lead are welded by using an ultrasonic welding method, they are housed in the battery can while the long and thin cathode lead is folded. Since the welding operation is generally performed at the outside of the battery can, the cathode lead must be designed to have an enough length to extend outside of the battery can.
However, the housing step of folding such a long lead within the battery can requires skill so as not to cause a short circuit accident, thus the skill-needed folding operation is not suitable for mass production. Furthermore, the foregoing housing step makes it difficult to achieve a high reliability of the product.
An object of the present invention is therefore to provide a non-aqueous electrolyte secondary battery having a structure which facilitates fabrication and is suitable for mass production, and further, which has high reliability, and a method of manufacturing the same.
According to a non-aqueous electrolyte secondary battery of the present invention, the secondary battery has such a structure that an inner lead of a rolled battery element housed in a container is electrically connected to an external terminal member provided at a sealing side of the container through an relay member, and is characterized in that the connecting member is designed so as to pressurize and fix a winding core of the rolled battery element, and includes a protruding surface enabling electrical connection between the connecting member and the inner lead by pressing the inner lead to an end face of the winding core.
Especially, for the purpose of facilitating a welding operation of the inner lead, it is preferable that the end face of the winding core protrudes from a winding end face of the battery element to a side of the protruding surface of the connecting member. Besides, it is preferable to provide a plurality of inner leads since inner resistance can be lowered.
It is also a feature that the conductive connecting member includes an annular flange structure along an inner periphery of the container at a side separate from the protruding surface. Besides, it is a feature that a heat-resistant member is joined with the end face of the winding core.
Moreover, according to the present invention, a method of manufacturing a non-aqueous electrolyte secondary battery comprises a step of housing a rolled battery element including a winding core at a center portion, a cathode side lead, and an anode inner lead into a container for a battery can so that an end face of the winding core is exposed at a sealing side, a step of disposing one side of the inner lead on the end face of the winding core and joining the one side of the inner lead to a protruding surface of a conductive connecting member using the end face of the winding core as abase, and a step of disposing and sealing an external terminal member at:the sealing side of the container so that the external terminal member is electrically connected to an end portion of the conductive connecting member.
This manufacturing method is also characterized in that the joining step is ultrasonic welding, the method further comprises a step of forming a support protrusion portion for supporting the conductive connecting member at an inner surface of the container prior to the ultrasonic welding step, and the ultrasonic welding is performed in a state where the conductive connecting member is held by the support protrusion portion. Moreover, this method is characterized in that a cylindrical gasket is provided between the support protrusion portion and the conductive connecting member, and in that the method further comprises a step of disposing the external terminal member on the conductive connecting member through a safety vent at an inner side of the gasket, and a step of joining the external terminal member, the safety vent, and the conductive connecting member by crimping an open end of the container together with the gasket. Moreover, the method is characterized by comprising a step of forming a base by joining a heat-resistant member to the end face of the winding core prior to positioning the inner lead on the end face of the winding core, and a step of folding and disposing the inner lead on the heat-resistant member.
Particularly, according to the present invention, there is provided a method of manufacturing a non-aqueous electrolyte secondary battery including a battery element housed in a battery can, the battery element being constructed by forming a cathode active material layer and an anode active material layer on a cathode collecting body and an anode collecting body, respectively, and laminating and winding them through a separator, the method of manufacturing the non-aqueous electrolyte secondary battery comprising the steps of folding part, to be jointed, of a plurality of electrode leads joined to the battery element housed in the battery can so as to be positioned at an upper end portion of a winding core of the battery component, putting a conductive connecting member on a gasket fixed to an upper portion of the battery can, welding the part, to be joined, of the plurality of electrode leads to a joint portion of the conductive connecting member while the upper end portion of the winding core is used as a base, and sealing the battery can in a state where the conductive connecting member is brought into contact with a battery header.